In plasma processing, plasmas create species such as radicals, excited molecular species, molecular fragments, individual atoms and/or free electrons from a source gas. Mixtures of such species, with or without untransformed portions of the source gas, and with or without further gases mixed in, are called “plasma products” herein. Plasma processing brings plasma products into contact with workpieces that may be, for example, semiconductor wafers. To create and/or maintain a plasma, one or more radio frequency (RF) and/or microwave generators typically provide electromagnetic power to a region that contains the source gas. The plasma can be generated from the source gas in the location of one or more wafers being processed, and/or in a first, “upstream” location, after which the plasma products move to a second, “downstream” location to contact the wafer(s). Some systems generate one, two or more plasmas in different locations before the plasma products ultimately contact the wafer(s). Source gases, plasma products and/or other gases mixed with the plasma products often contain highly energetic, charged and/or corrosive species, and/or highly energetic electrons, such that the plasma equipment can sometimes degrade from contact with these materials. This can make materials and/or coatings of plasma system components critical to the longevity and maintenance requirements of the system. Wafer processing can also be affected, and therefore controlled by, the relative presence or absence of certain components of plasma products.